1. Field of the Invention
The present invention relates to blocking devices for hollow structures. In particular, the present invention relates to blocking devices for improving the damping and sound insulating properties of hollow panel structures, such as pillars, rocker panels, and roof side panels of automobile bodies. The hollow panel structures are each formed by a plurality of panels to have a closed cross-sectional area.
2. Description of the Related Art
A known blocking device has a holder mounted within a space defined within a hollow structure and an expandable member that is supported by the holder. The expandable member may be externally heated to expand so as to form a foam member. The holder includes a holder plate and a mounting device for mounting to the hollow structure. The holder plate is positioned within the space and extends substantially perpendicular to the longitudinal direction of the hollow structure. The holder plate typically supports at least one side of the expandable member.
In order to provide effective blocking, for example, Japanese Laid-Open Patent Publication No. 10-91170 teaches a blocking device having an annular portion formed on the entire expandable member or on at least a part of the expandable member. The blocking device also has an annular wall formed on a holder plate in order to support the inner peripheral surface of the annular portion of the expandable member.
However, in some cases, the expandable member of the above publication has a fragile region(s) at the annular portion or at a portion(s) having a narrow width. For example, in the event that the expandable member is molded by an injection molding process, a weld line may be produced at a portion where the flows of the molten material of the expandable member converge. Such a weld line may form a fragile region that tends to be easily torn.
Therefore, at the beginning of the external heating process of the formed extendable base member, the heated extendable base member may be torn at the fragile region (e.g. weld line) due to initial softening and constriction of the foam member before expansion of the foam member. When this occurs, a problem may be caused in which a gap is produced between the torn region and the inner peripheral wall of the space due to short charge of the material (i.e., an inadequate amount of material). As a result, the space may not be effectively blocked.
Even in the event that that expandable member is formed by a sheet punching process, the problem of non-effective blocking may still exist. The annular portion or the narrow width portion may form a fragile region that may be torn or broken before the expandable member is expanded.